No. 4: Michael Vick

Quarterback Michael Vick's record-breaking $130 million contract extension and product endorsements earned him a spot in 2005 on Forbes' Top 100 Celebrities list, but just two years later, his career came to a sudden, ignominious halt.

Vick was among four men charged in an interstate dog-fighting ring known as "Bad Newz Kennels." He pleaded guilty in 2007 to conspiracy to operate an interstate dog-fighting ring but denied killing any of the dogs himself.

Vick, now 28, is serving a 23-month sentence in federal prison and is expected to enter a federal halfway house program early next year. He may attempt an NFL comeback after his release, and he may have to — after filing for bankruptcy in July.